1. Field of the Invention:
The present invention relates to measurement of positions of objects, and more particularly concerns measurement of angular relations. Methods and apparatus of this invention may be employed for measurements of vectors, that is, the measurement of either one or both of the direction and coordinate position of a vector with respect to a reference system.
2. Description of Prior Art
Position measuring instruments are employed in a wide variety of manufacturing, assembly and inspection operations. Generally, one or a number of different points on an object to be measured are contacted by a probe that is movable with respect to a reference coordinate system. Most commonly, the probe is mounted for translational motion along three coordinate axes as, for example, in the machines shown in U.S. Pat. Nos. 3,774,311 to Stemple and 3,774,312 to Esch. These machines are of limited application because the size of the machine itself determines the size of the object that may be measured, and costs increase rapidly with increasing size. Because of the difficulties of maintaining precision of position and motion in traveling over long cantilevered elements, such devices must be exceedingly massive for required rigidity. Further, they often require complex techniques such as the impressed vibratory movement of the Esch patent or unique and expensive bearing structures of the Stemple patent for obtaining desired precision. Even so, such machines measure only a point, by determining its coordinates. Therefore, two separate and independent measurements at spaced points are needed for measuring direction. Further, if the angular relation of a planar surface is to be measured, as for example, in determining a normal to a surface, machines of the prior art require three separate measurements to define the plane.
The U.S. Pat. to Bower, No. 2,906,179, describes a coordinate position measuring gauge comprising several pivotally interconnected links of adjustable length. Although the Bower gauge is illustrated in connection with a closed loop control system for a machining tool, it still can provide information defining solely the coordinate position of a single point for any given measurement.
In the prior art of measuring instruments, optical devices have been employed for alignment of parts or, in effect, measuring direction. Thus, an autocollinator, such as shown in U.S. Pat. No. 3,024,365 to Smith et al has been employed for remote measurement of the orientation of a reflective surface, as used for example, in the alignment of an autonavigator. However, such optical devices, like theodolites and precision transits, require careful and exact positioning or setup to achieve a predetermined and therefore, fixed position of alignment. For measurement of some second or different direction such optical measuring or alignment devices must be moved and the precision instrument setup carefully re-established prior to a second measurement.
In various types of tube bending machines, such as in that described in the U.S. Pat. to Hill No. 3,145,756, or that described in the U.S. Pat. to Hautau No. 3,299,681, various measurements must be made upon the straight portions (straights) of bent tubes to obtain information for computation of machine bending commands or to obtain information for making various corrections to the tube machine bending commands. As shown in the British Pat. No. 1,329,708 to McMurtry, for example, bent tubes or pipes are made from previously bent master pipes, employing a three-axis coordinate point measuring gauge which measures the position of two stations on each straight portion of the tube in cartesian coordinates. The working head of this coordinate point measuring machine, much like the working head of other three axis measuring machines, will contact a point on the object to be measured but does not attain any predetermined angular position or direction with respect to the object to be measured. Therefore, it is not possible to measure a vector or direction without making several measurements.
Accordingly, it is an object of the present invention to enable measurement of direction of a line having a fixed angular relation with respect to an object.